Search results for "liquid"
showing 10 items of 4351 documents
Purification and characterization of leucine aminopeptidase from kidney bean cotyledons
1992
A leucine aminopeptidase (EC 3,4,11.1) was purified from cotyledons of resting kidney beans (Phaseolus vulgaris L. cv. Processor) by acidic extraction, ammonium sulfate fractionation and chromatography on DEAE-Sephacel, Sephacryl S-300, Mono Q HPLC and Superose HPLC columns. The yield of the 317-fold purified enzyme was 9%. On gel filtrations on Sephacryl S-300 and Superose HPLC the elution volumes of the enzyme corresponded to an M, of 360 000. The enzyme gave one band on native gel electrophoresis and an electrophoretic titration in an immobilized pH gradient gave a single curve with a pI of 4.8. Two bands were observed in an SDS-gel electrophoresis with Mr values of 58 000 and 60 000 bot…
Lattice fluid model generalized for specific interactions: An application to ternary polymer solutions
2011
Abstract The phase diagram of the Poly- l -Lactic-Acid (PLLA), dioxane and water system was derived by using the lattice fluid model generalized for specific interactions. A qualitative analysis of Hansen solubility parameters together with empirical observations were adopted to reduce the number of adjustable parameters. The as-selected model parameters were derived by fitting a set of cloud point curves; consequently, the complete phase diagram of the system was computed. The use of specific interactions between species gave out a quantitative agreement with a set of experimental data, whereas changing the polymer polydispersity the agreement is only qualitative. In principle, the present…
Synthesis and Characterization of a New Class of Fully Aromatic Liquid Crystal Polymers
1999
Abstract A new fully aromatic LCP, obtained by polycondensation of N-(4-carboxyphenyl) trimellitimide and tert-butyl hydroquinone (FAPT), was previously described. The polymer shows very interesting physical and mechanical properties but a very high glass transition temperature which does not allow a good processability. In order to overcome this problem, a new class of LCPs, obtained by partial substitution of the dicarboxylic moiety with isophthalic acid, is described. The new thermoplastic materials were characterized from the physicochemical and mechanical point of view. All the polymers obtained with an isophthalic acid (FA-IA) content varying from 10 to 40% of the substituted moiety s…
New ferrocene-containing copolyesters
1995
We have synthesized four new ferrocene monomers (three diols and one diester). The redox potential of these ferrocene derivatives varies between 0 mV and 230 mV due to different degrees of ring alkylation. Amorphous and liquid crystalline copolyesters were prepared with these monomers in the polymer main chain. Cyclovoltammetric measurements show that the redox potential of the ferrocene units is increased by about 40 mV upon polymer formation (esterification). Since the ester group is 4 to 6 σ-bonds away from the ferrocene unit this increase is probably caused by some charge-transfer interaction through space. First rheological measurements show an unusual rubber-like behaviour of the ferr…
Persistent photovoltage in methylammonium lead iodide perovskite solar cells
2014
Open circuit voltage decay measurements are performed on methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells to investigate the charge carrier recombination dynamics. The measurements are compared to the two reference polymer-fullerene bulk heterojunction solar cells based on P3HT:PC60BM and PTB7:PC70BM blends. In the perovskite devices, two very different time domains of the voltage decay are found, with a first drop on a short time scale that is similar to the organic solar cells. However, two major differences are also observed. 65-70% of the maximum photovoltage persists on much longer timescales, and the recombination dynamics are dependent on the illumination intensity.
Surface anchoring on liquid crystalline polymer brushes
2002
We present a Monte Carlo study of the surface anchoring of a nematic fluid on swollen layers of grafted liquid crystalline chain molecules. The liquid crystalline particles are modeled by soft repulsive ellipsoids, and the chains are made of the same particles. An appropriately modified version of the configurational bias Monte Carlo algorithm is introduced, which removes and redistributes chain bonds rather than whole monomers. With this algorithm, a wide range of grafting densities could be studied. The substrate is chosen such that it favors a planar orientation (parallel to the surface). Depending on the grafting density, we find three anchoring regimes: planar, tilted, and perpendicula…
Heterogeneity at the glass transition: a review
1999
Theoretical concepts and experimental evidence of heterogeneity in glass-forming liquids and polymers are reviewed. The main purpose is to provide an introduction to theoretical developments and recent experiments which have led to rapidly increasing knowledge. Realizing that there is no consensus in regard to the various scenarios of the glass transition starting from rather different assumptions we try to give a balanced overview although we also compare and interrelate some of the approaches. The experimental part describes recent nuclear magnetic resonance, dielectric, and optical experiments from which dynamically distinguishable subensembles can be selected thus proving the existence …
Electroactive Liquid Crystalline Polymers ☆
2017
As with low molecular mass liquid crystals, the polymeric liquid crystalline compounds show many possibilities for interaction with electrical fields. Charge transport via the aromatic cores allows the construction of light emitting devices, field effect transistors and photovoltaic cells. The order of the liquid crystalline phases helps to improve intramolecular charge transfer and the mobility allows easy alignment. Liquid crystalline polymers with ferroelectric phases can be used in fast switching optical devices. Their unique switching mechanism proceeds under reduced interaction with the polymer chains. The combination of liquid crystallinity with elastomer networks leads to electromec…
Analysis of amino acids using serially coupled columns.
2017
Single conventional columns in reversed-phase LC are insufficient for analysing the isoindoles of primary amino acids, due to their limited functionality. An interesting possibility for increasing the separation power is the combination of several columns of different nature, where the length is modified by coupling small segments. This approach may require a considerable investment to have multiple lengths for each stationary phase. However, the combination of only two columns of fixed length can be enough to resolve satisfactorily relatively complex mixtures, provided that an optimised gradient program is applied. In this work, a mixture of 19 primary amino acid isoindoles found in protei…
Structure and Dynamics of Liquid Crystalline Polymers from Deuteron NMR
1983
The molecular structures of thermotropic liquid crystalline polymers, which have been synthesized systematically in recent years, are described according to the model of decoupling the molecular motions of the mesogenic groups and the polymer chain by inserting a flexible spacer. The molecular structure is related to the properties of these systems, e.g., phase transition temperatures, mesophases formed, etc. The structure and mobility of a specific side chain, liquid crystalline polyacrylate with phenyl benzoate as a mesogenic group is investigated by deuteron NMR and compared with the behaviour of low molecular weight analogues selectively deuterated at equivalent positions, i.e., at the …